1. Field of the Invention
The present invention relates to an organic electroluminescent device that has a long lifetime.
2. Description of the Related Art
Organic electroluminescent devices are self-emissive devices that emit light when a current is applied to a fluorescent or phosphorescent organic layer through the combination of electrons and holes in the organic layer. Organic electroluminescent devices have many advantages including being light weight, easy to manufacture, having high resolution, and having wide viewing angles. In addition, organic electroluminescent devices can display moving pictures with high color purity, and have low power consumption and a low driving voltage. These advantages make organic electroluminescent devices suitable for use in portable electronics.
Generally, in order to improve efficiency and decrease the driving voltage, an organic electroluminescent device comprises an emission layer, an electron transport layer, and a hole transport layer, all of which are organic layers. Many factors affect lifetime, efficiency, a driving voltage, color coordinates, of the organic electroluminescent device. Such factors include the thickness of the individual organic layers, the concentration of a dopant in the emission layer, and the total thickness of all of the organic layers.
In order to emit green light, the emission layer may comprise Alq3. However, when the emission layer is composed of only Alq3, excess holes are generated such that the emission layer deteriorates, thus decreasing the lifetime of the device. The holes combine with a pair of unshared electrons of oxygen of Alq3, thus altering the stable structure of Alq3. The changed stable structure of Alq3 results in a deterioration of the emission layer.